#
# Copyright 2021 ThoughtWorks, Inc.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
#

module PrototypeHelper
  include ActionView::Helpers::JavaScriptHelper

    unless const_defined? :CALLBACKS
    CALLBACKS    = Set.new([ :create, :uninitialized, :loading, :loaded,
                             :interactive, :complete, :failure, :success ] +
                               (100..599).to_a)
    AJAX_OPTIONS = Set.new([ :before, :after, :condition, :url,
                             :asynchronous, :method, :insertion, :position,
                             :form, :with, :update, :script, :type ]).merge(CALLBACKS)
  end

  # Returns a link to a remote action defined by <tt>options[:url]</tt>
  # (using the url_for format) that's called in the background using
  # XMLHttpRequest. The result of that request can then be inserted into a
  # DOM object whose id can be specified with <tt>options[:update]</tt>.
  # Usually, the result would be a partial prepared by the controller with
  # render :partial.
  #
  # Examples:
  #   # Generates: <a href="#" onclick="new Ajax.Updater('posts', '/blog/destroy/3', {asynchronous:true, evalScripts:true});
  #   #            return false;">Delete this post</a>
  #   link_to_remote "Delete this post", :update => "posts",
  #     :url => { :action => "destroy", :id => post.id }
  #
  #   # Generates: <a href="#" onclick="new Ajax.Updater('emails', '/mail/list_emails', {asynchronous:true, evalScripts:true});
  #   #            return false;"><img alt="Refresh" src="/images/refresh.png?" /></a>
  #   link_to_remote(image_tag("refresh"), :update => "emails",
  #     :url => { :action => "list_emails" })
  #
  # You can override the generated HTML options by specifying a hash in
  # <tt>options[:html]</tt>.
  #
  #   link_to_remote "Delete this post", :update => "posts",
  #     :url  => post_url(@post), :method => :delete,
  #     :html => { :class  => "destructive" }
  #
  # You can also specify a hash for <tt>options[:update]</tt> to allow for
  # easy redirection of output to an other DOM element if a server-side
  # error occurs:
  #
  # Example:
  #   # Generates: <a href="#" onclick="new Ajax.Updater({success:'posts',failure:'error'}, '/blog/destroy/5',
  #   #            {asynchronous:true, evalScripts:true}); return false;">Delete this post</a>
  #   link_to_remote "Delete this post",
  #     :url => { :action => "destroy", :id => post.id },
  #     :update => { :success => "posts", :failure => "error" }
  #
  # Optionally, you can use the <tt>options[:position]</tt> parameter to
  # influence how the target DOM element is updated. It must be one of
  # <tt>:before</tt>, <tt>:top</tt>, <tt>:bottom</tt>, or <tt>:after</tt>.
  #
  # The method used is by default POST. You can also specify GET or you
  # can simulate PUT or DELETE over POST. All specified with <tt>options[:method]</tt>
  #
  # Example:
  #   # Generates: <a href="#" onclick="new Ajax.Request('/person/4', {asynchronous:true, evalScripts:true, method:'delete'});
  #   #            return false;">Destroy</a>
  #   link_to_remote "Destroy", :url => person_url(:id => person), :method => :delete
  #
  # By default, these remote requests are processed asynchronous during
  # which various JavaScript callbacks can be triggered (for progress
  # indicators and the likes). All callbacks get access to the
  # <tt>request</tt> object, which holds the underlying XMLHttpRequest.
  #
  # To access the server response, use <tt>request.responseText</tt>, to
  # find out the HTTP status, use <tt>request.status</tt>.
  #
  # Example:
  #   # Generates: <a href="#" onclick="new Ajax.Request('/words/undo?n=33', {asynchronous:true, evalScripts:true,
  #   #            onComplete:function(request){undoRequestCompleted(request)}}); return false;">hello</a>
  #   word = 'hello'
  #   link_to_remote word,
  #     :url => { :action => "undo", :n => word_counter },
  #     :complete => "undoRequestCompleted(request)"
  #
  # The callbacks that may be specified are (in order):
  #
  # <tt>:loading</tt>::       Called when the remote document is being
  #                           loaded with data by the browser.
  # <tt>:loaded</tt>::        Called when the browser has finished loading
  #                           the remote document.
  # <tt>:interactive</tt>::   Called when the user can interact with the
  #                           remote document, even though it has not
  #                           finished loading.
  # <tt>:success</tt>::       Called when the XMLHttpRequest is completed,
  #                           and the HTTP status code is in the 2XX range.
  # <tt>:failure</tt>::       Called when the XMLHttpRequest is completed,
  #                           and the HTTP status code is not in the 2XX
  #                           range.
  # <tt>:complete</tt>::      Called when the XMLHttpRequest is complete
  #                           (fires after success/failure if they are
  #                           present).
  #
  # You can further refine <tt>:success</tt> and <tt>:failure</tt> by
  # adding additional callbacks for specific status codes.
  #
  # Example:
  #   # Generates: <a href="#" onclick="new Ajax.Request('/testing/action', {asynchronous:true, evalScripts:true,
  #   #            on404:function(request){alert('Not found...? Wrong URL...?')},
  #   #            onFailure:function(request){alert('HTTP Error ' + request.status + '!')}}); return false;">hello</a>
  #   link_to_remote word,
  #     :url => { :action => "action" },
  #     404 => "alert('Not found...? Wrong URL...?')",
  #     :failure => "alert('HTTP Error ' + request.status + '!')"
  #
  # A status code callback overrides the success/failure handlers if
  # present.
  #
  # If you for some reason or another need synchronous processing (that'll
  # block the browser while the request is happening), you can specify
  # <tt>options[:type] = :synchronous</tt>.
  #
  # You can customize further browser side call logic by passing in
  # JavaScript code snippets via some optional parameters. In their order
  # of use these are:
  #
  # <tt>:confirm</tt>::      Adds confirmation dialog.
  # <tt>:condition</tt>::    Perform remote request conditionally
  #                          by this expression. Use this to
  #                          describe browser-side conditions when
  #                          request should not be initiated.
  # <tt>:before</tt>::       Called before request is initiated.
  # <tt>:after</tt>::        Called immediately after request was
  #                          initiated and before <tt>:loading</tt>.
  # <tt>:submit</tt>::       Specifies the DOM element ID that's used
  #                          as the parent of the form elements. By
  #                          default this is the current form, but
  #                          it could just as well be the ID of a
  #                          table row or any other DOM element.
  # <tt>:with</tt>::         A JavaScript expression specifying
  #                          the parameters for the XMLHttpRequest.
  #                          Any expressions should return a valid
  #                          URL query string.
  #
  #                          Example:
  #
  #                            :with => "'name=' + $('name').value"
  #
  # You can generate a link that uses AJAX in the general case, while
  # degrading gracefully to plain link behavior in the absence of
  # JavaScript by setting <tt>html_options[:href]</tt> to an alternate URL.
  # Note the extra curly braces around the <tt>options</tt> hash separate
  # it as the second parameter from <tt>html_options</tt>, the third.
  #
  # Example:
  #   link_to_remote "Delete this post",
  #     { :update => "posts", :url => { :action => "destroy", :id => post.id } },
  #     :href => url_for(:action => "destroy", :id => post.id)
  def link_to_remote(name, options = {}, html_options = nil)
    link_to_function(name, remote_function(options), html_options || options.delete(:html))
  end

  # Creates a button with an onclick event which calls a remote action
  # via XMLHttpRequest
  # The options for specifying the target with :url
  # and defining callbacks is the same as link_to_remote.
  def button_to_remote(name, options = {}, html_options = {})
    button_to_function(name, remote_function(options), html_options)
  end

  # Periodically calls the specified url (<tt>options[:url]</tt>) every
  # <tt>options[:frequency]</tt> seconds (default is 10). Usually used to
  # update a specified div (<tt>options[:update]</tt>) with the results
  # of the remote call. The options for specifying the target with <tt>:url</tt>
  # and defining callbacks is the same as link_to_remote.
  # Examples:
  #  # Call get_averages and put its results in 'avg' every 10 seconds
  #  # Generates:
  #  #      new PeriodicalExecuter(function() {new Ajax.Updater('avg', '/grades/get_averages',
  #  #      {asynchronous:true, evalScripts:true})}, 10)
  #  periodically_call_remote(:url => { :action => 'get_averages' }, :update => 'avg')
  #
  #  # Call invoice every 10 seconds with the id of the customer
  #  # If it succeeds, update the invoice DIV; if it fails, update the error DIV
  #  # Generates:
  #  #      new PeriodicalExecuter(function() {new Ajax.Updater({success:'invoice',failure:'error'},
  #  #      '/testing/invoice/16', {asynchronous:true, evalScripts:true})}, 10)
  #  periodically_call_remote(:url => { :action => 'invoice', :id => customer.id },
  #     :update => { :success => "invoice", :failure => "error" }
  #
  #  # Call update every 20 seconds and update the new_block DIV
  #  # Generates:
  #  # new PeriodicalExecuter(function() {new Ajax.Updater('news_block', 'update', {asynchronous:true, evalScripts:true})}, 20)
  #  periodically_call_remote(:url => 'update', :frequency => '20', :update => 'news_block')
  #
  def periodically_call_remote(options = {})
    frequency = options[:frequency] || 10 # every ten seconds by default
    code = "new PeriodicalExecuter(function() {#{remote_function(options)}}, #{frequency})"
    javascript_tag(code)
  end

  # Returns a form tag that will submit using XMLHttpRequest in the
  # background instead of the regular reloading POST arrangement. Even
  # though it's using JavaScript to serialize the form elements, the form
  # submission will work just like a regular submission as viewed by the
  # receiving side (all elements available in <tt>params</tt>). The options for
  # specifying the target with <tt>:url</tt> and defining callbacks is the same as
  # +link_to_remote+.
  #
  # A "fall-through" target for browsers that doesn't do JavaScript can be
  # specified with the <tt>:action</tt>/<tt>:method</tt> options on <tt>:html</tt>.
  #
  # Example:
  #   # Generates:
  #   #      <form action="/some/place" method="post" onsubmit="new Ajax.Request('',
  #   #      {asynchronous:true, evalScripts:true, parameters:Form.serialize(this)}); return false;">
  #   form_remote_tag :html => { :action =>
  #     url_for(:controller => "some", :action => "place") }
  #
  # The Hash passed to the <tt>:html</tt> key is equivalent to the options (2nd)
  # argument in the FormTagHelper.form_tag method.
  #
  # By default the fall-through action is the same as the one specified in
  # the <tt>:url</tt> (and the default method is <tt>:post</tt>).
  #
  # form_remote_tag also takes a block, like form_tag:
  #   # Generates:
  #   #     <form action="/" method="post" onsubmit="new Ajax.Request('/',
  #   #     {asynchronous:true, evalScripts:true, parameters:Form.serialize(this)});
  #   #     return false;"> <div><input name="commit" type="submit" value="Save" /></div>
  #   #     </form>
  #   <% form_remote_tag :url => '/posts' do -%>
  #     <div><%= submit_tag 'Save' %></div>
  #   <% end -%>
  def form_remote_tag(options = {}, &block)
    options[:form] = true

    options[:html] ||= {}
    options[:html][:onsubmit] =
        (options[:html][:onsubmit] ? options[:html][:onsubmit] + "; " : "") +
            "#{remote_function(options)}; return false;"

    form_tag(options[:html].delete(:action) || url_for(options[:url]), options[:html], &block)
  end

  # Creates a form that will submit using XMLHttpRequest in the background
  # instead of the regular reloading POST arrangement and a scope around a
  # specific resource that is used as a base for questioning about
  # values for the fields.
  #
  # === Resource
  #
  # Example:
  #   <% remote_form_for(@post) do |f| %>
  #     ...
  #   <% end %>
  #
  # This will expand to be the same as:
  #
  #   <% remote_form_for :post, @post, :url => post_path(@post), :html => { :method => :put, :class => "edit_post", :id => "edit_post_45" } do |f| %>
  #     ...
  #   <% end %>
  #
  # === Nested Resource
  #
  # Example:
  #   <% remote_form_for([@post, @comment]) do |f| %>
  #     ...
  #   <% end %>
  #
  # This will expand to be the same as:
  #
  #   <% remote_form_for :comment, @comment, :url => post_comment_path(@post, @comment), :html => { :method => :put, :class => "edit_comment", :id => "edit_comment_45" } do |f| %>
  #     ...
  #   <% end %>
  #
  # If you don't need to attach a form to a resource, then check out form_remote_tag.
  #
  # See FormHelper#form_for for additional semantics.
  def remote_form_for(record_or_name_or_array, *args, &proc)
    options = args.extract_options!

    case record_or_name_or_array
      when String, Symbol
        object_name = record_or_name_or_array
      when Array
        object = record_or_name_or_array.last
        object_name = ActionController::RecordIdentifier.singular_class_name(object)
        apply_form_for_options!(record_or_name_or_array, options)
        args.unshift object
      else
        object      = record_or_name_or_array
        object_name = ActionController::RecordIdentifier.singular_class_name(record_or_name_or_array)
        apply_form_for_options!(object, options)
        args.unshift object
    end

    concat(form_remote_tag(options))
    fields_for(object_name, *(args << options), &proc)
    concat('</form>')
  end
  alias_method :form_remote_for, :remote_form_for

  # Returns a button input tag with the element name of +name+ and a value (i.e., display text) of +value+
  # that will submit form using XMLHttpRequest in the background instead of a regular POST request that
  # reloads the page.
  #
  #  # Create a button that submits to the create action
  #  #
  #  # Generates: <input name="create_btn" onclick="new Ajax.Request('/testing/create',
  #  #     {asynchronous:true, evalScripts:true, parameters:Form.serialize(this.form)});
  #  #     return false;" type="button" value="Create" />
  #  <%= submit_to_remote 'create_btn', 'Create', :url => { :action => 'create' } %>
  #
  #  # Submit to the remote action update and update the DIV succeed or fail based
  #  # on the success or failure of the request
  #  #
  #  # Generates: <input name="update_btn" onclick="new Ajax.Updater({success:'succeed',failure:'fail'},
  #  #      '/testing/update', {asynchronous:true, evalScripts:true, parameters:Form.serialize(this.form)});
  #  #      return false;" type="button" value="Update" />
  #  <%= submit_to_remote 'update_btn', 'Update', :url => { :action => 'update' },
  #     :update => { :success => "succeed", :failure => "fail" }
  #
  # <tt>options</tt> argument is the same as in form_remote_tag.
  def submit_to_remote(name, value, options = {})
    options[:with] ||= 'Form.serialize(this.form)'

    html_options = options.delete(:html) || {}
    html_options[:name] = name

    button_to_remote(value, options, html_options)
  end

  # Returns '<tt>eval(request.responseText)</tt>' which is the JavaScript function
  # that +form_remote_tag+ can call in <tt>:complete</tt> to evaluate a multiple
  # update return document using +update_element_function+ calls.
  def evaluate_remote_response
    "eval(request.responseText)"
  end

  # Returns the JavaScript needed for a remote function.
  # Takes the same arguments as link_to_remote.
  #
  # Example:
  #   # Generates: <select id="options" onchange="new Ajax.Updater('options',
  #   # '/testing/update_options', {asynchronous:true, evalScripts:true})">
  #   <select id="options" onchange="<%= remote_function(:update => "options",
  #       :url => { :action => :update_options }) %>">
  #     <option value="0">Hello</option>
  #     <option value="1">World</option>
  #   </select>
  def remote_function(options)
    javascript_options = options_for_ajax(options)

    update = ''
    if options[:update] && options[:update].is_a?(Hash)
      update  = []
      update << "success:'#{options[:update][:success]}'" if options[:update][:success]
      update << "failure:'#{options[:update][:failure]}'" if options[:update][:failure]
      update  = '{' + update.join(',') + '}'
    elsif options[:update]
      update << "'#{options[:update]}'"
    end

    function = update.empty? ?
        "new Ajax.Request(" :
        "new Ajax.Updater(#{update}, "

    url_options = options[:url]
    url_options = url_options.merge(:escape => false) if url_options.is_a?(Hash)
    function << "'#{escape_javascript(url_for(url_options))}'"
    function << ", #{javascript_options})"

    function = "#{options[:before]}; #{function}" if options[:before]
    function = "#{function}; #{options[:after]}"  if options[:after]
    function = "if (#{options[:condition]}) { #{function}; }" if options[:condition]
    function = "if (confirm('#{escape_javascript(options[:confirm])}')) { #{function}; }" if options[:confirm]

    return function
  end

  # Observes the field with the DOM ID specified by +field_id+ and calls a
  # callback when its contents have changed. The default callback is an
  # Ajax call. By default the value of the observed field is sent as a
  # parameter with the Ajax call.
  #
  # Example:
  #  # Generates: new Form.Element.Observer('suggest', 0.25, function(element, value) {new Ajax.Updater('suggest',
  #  #         '/testing/find_suggestion', {asynchronous:true, evalScripts:true, parameters:'q=' + value})})
  #  <%= observe_field :suggest, :url => { :action => :find_suggestion },
  #       :frequency => 0.25,
  #       :update => :suggest,
  #       :with => 'q'
  #       %>
  #
  # Required +options+ are either of:
  # <tt>:url</tt>::       +url_for+-style options for the action to call
  #                       when the field has changed.
  # <tt>:function</tt>::  Instead of making a remote call to a URL, you
  #                       can specify javascript code to be called instead.
  #                       Note that the value of this option is used as the
  #                       *body* of the javascript function, a function definition
  #                       with parameters named element and value will be generated for you
  #                       for example:
  #                         observe_field("glass", :frequency => 1, :function => "alert('Element changed')")
  #                       will generate:
  #                         new Form.Element.Observer('glass', 1, function(element, value) {alert('Element changed')})
  #                       The element parameter is the DOM element being observed, and the value is its value at the
  #                       time the observer is triggered.
  #
  # Additional options are:
  # <tt>:frequency</tt>:: The frequency (in seconds) at which changes to
  #                       this field will be detected. Not setting this
  #                       option at all or to a value equal to or less than
  #                       zero will use event based observation instead of
  #                       time based observation.
  # <tt>:update</tt>::    Specifies the DOM ID of the element whose
  #                       innerHTML should be updated with the
  #                       XMLHttpRequest response text.
  # <tt>:with</tt>::      A JavaScript expression specifying the parameters
  #                       for the XMLHttpRequest. The default is to send the
  #                       key and value of the observed field. Any custom
  #                       expressions should return a valid URL query string.
  #                       The value of the field is stored in the JavaScript
  #                       variable +value+.
  #
  #                       Examples
  #
  #                         :with => "'my_custom_key=' + value"
  #                         :with => "'person[name]=' + prompt('New name')"
  #                         :with => "Form.Element.serialize('other-field')"
  #
  #                       Finally
  #                         :with => 'name'
  #                       is shorthand for
  #                         :with => "'name=' + value"
  #                       This essentially just changes the key of the parameter.
  #
  # Additionally, you may specify any of the options documented in the
  # <em>Common options</em> section at the top of this document.
  #
  # Example:
  #
  #   # Sends params: {:title => 'Title of the book'} when the book_title input
  #   # field is changed.
  #   observe_field 'book_title',
  #     :url => 'http://example.com/books/edit/1',
  #     :with => 'title'
  #
  #
  def observe_field(field_id, options = {})
    if options[:frequency] && options[:frequency] > 0
      build_observer('Form.Element.Observer', field_id, options)
    else
      build_observer('Form.Element.EventObserver', field_id, options)
    end
  end

  # Observes the form with the DOM ID specified by +form_id+ and calls a
  # callback when its contents have changed. The default callback is an
  # Ajax call. By default all fields of the observed field are sent as
  # parameters with the Ajax call.
  #
  # The +options+ for +observe_form+ are the same as the options for
  # +observe_field+. The JavaScript variable +value+ available to the
  # <tt>:with</tt> option is set to the serialized form by default.
  def observe_form(form_id, options = {})
    if options[:frequency]
      build_observer('Form.Observer', form_id, options)
    else
      build_observer('Form.EventObserver', form_id, options)
    end
  end

  # All the methods were moved to GeneratorMethods so that
  # #include_helpers_from_context has nothing to overwrite.
  class JavaScriptGenerator #:nodoc:
    def initialize(context, &block) #:nodoc:
      @context, @lines = context, []
      include_helpers_from_context
      @context.with_output_buffer(@lines) do
        @context.instance_exec(self, &block)
      end
    end

    private
    def include_helpers_from_context
      extend @context.helpers if @context.respond_to?(:helpers)
      extend GeneratorMethods
    end

    # JavaScriptGenerator generates blocks of JavaScript code that allow you
    # to change the content and presentation of multiple DOM elements.  Use
    # this in your Ajax response bodies, either in a <script> tag or as plain
    # JavaScript sent with a Content-type of "text/javascript".
    #
    # Create new instances with PrototypeHelper#update_page or with
    # ActionController::Base#render, then call +insert_html+, +replace_html+,
    # +remove+, +show+, +hide+, +visual_effect+, or any other of the built-in
    # methods on the yielded generator in any order you like to modify the
    # content and appearance of the current page.
    #
    # Example:
    #
    #   # Generates:
    #   #     new Element.insert("list", { bottom: "<li>Some item</li>" });
    #   #     new Effect.Highlight("list");
    #   #     ["status-indicator", "cancel-link"].each(Element.hide);
    #   update_page do |page|
    #     page.insert_html :bottom, 'list', "<li>#{@item.name}</li>"
    #     page.visual_effect :highlight, 'list'
    #     page.hide 'status-indicator', 'cancel-link'
    #   end
    #
    #
    # Helper methods can be used in conjunction with JavaScriptGenerator.
    # When a helper method is called inside an update block on the +page+
    # object, that method will also have access to a +page+ object.
    #
    # Example:
    #
    #   module ApplicationHelper
    #     def update_time
    #       page.replace_html 'time', Time.now.to_s(:db)
    #       page.visual_effect :highlight, 'time'
    #     end
    #   end
    #
    #   # Controller action
    #   def poll
    #     render(:update) { |page| page.update_time }
    #   end
    #
    # Calls to JavaScriptGenerator not matching a helper method below
    # generate a proxy to the JavaScript Class named by the method called.
    #
    # Examples:
    #
    #   # Generates:
    #   #     Foo.init();
    #   update_page do |page|
    #     page.foo.init
    #   end
    #
    #   # Generates:
    #   #     Event.observe('one', 'click', function () {
    #   #       $('two').show();
    #   #     });
    #   update_page do |page|
    #     page.event.observe('one', 'click') do |p|
    #      p[:two].show
    #     end
    #   end
    #
    # You can also use PrototypeHelper#update_page_tag instead of
    # PrototypeHelper#update_page to wrap the generated JavaScript in a
    # <script> tag.
    module GeneratorMethods
      def to_s #:nodoc:
        returning javascript = @lines * $/ do
          if ActionView::Base.debug_rjs
            source = javascript.dup
            javascript.replace "try {\n#{source}\n} catch (e) "
            javascript << "{ alert('RJS error:\\n\\n' + e.toString()); alert('#{source.gsub('\\','\0\0').gsub(/\r\n|\n|\r/, "\\n").gsub(/["']/) { |m| "\\#{m}" }}'); throw e }"
          end
        end
      end

      # Returns a element reference by finding it through +id+ in the DOM. This element can then be
      # used for further method calls. Examples:
      #
      #   page['blank_slate']                  # => $('blank_slate');
      #   page['blank_slate'].show             # => $('blank_slate').show();
      #   page['blank_slate'].show('first').up # => $('blank_slate').show('first').up();
      #
      # You can also pass in a record, which will use ActionController::RecordIdentifier.dom_id to lookup
      # the correct id:
      #
      #   page[@post]     # => $('post_45')
      #   page[Post.new]  # => $('new_post')
      def [](id)
        case id
          when String, Symbol, NilClass
            JavaScriptElementProxy.new(self, id)
          else
            JavaScriptElementProxy.new(self, ActionController::RecordIdentifier.dom_id(id))
        end
      end

      # Returns an object whose <tt>to_json</tt> evaluates to +code+. Use this to pass a literal JavaScript
      # expression as an argument to another JavaScriptGenerator method.
      def literal(code)
        ::ActiveSupport::JSON::Variable.new(code.to_s)
      end

      # Returns a collection reference by finding it through a CSS +pattern+ in the DOM. This collection can then be
      # used for further method calls. Examples:
      #
      #   page.select('p')                      # => $$('p');
      #   page.select('p.welcome b').first      # => $$('p.welcome b').first();
      #   page.select('p.welcome b').first.hide # => $$('p.welcome b').first().hide();
      #
      # You can also use prototype enumerations with the collection.  Observe:
      #
      #   # Generates: $$('#items li').each(function(value) { value.hide(); });
      #   page.select('#items li').each do |value|
      #     value.hide
      #   end
      #
      # Though you can call the block param anything you want, they are always rendered in the
      # javascript as 'value, index.'  Other enumerations, like collect() return the last statement:
      #
      #   # Generates: var hidden = $$('#items li').collect(function(value, index) { return value.hide(); });
      #   page.select('#items li').collect('hidden') do |item|
      #     item.hide
      #   end
      #
      def select(pattern)
        JavaScriptElementCollectionProxy.new(self, pattern)
      end

      # Inserts HTML at the specified +position+ relative to the DOM element
      # identified by the given +id+.
      #
      # +position+ may be one of:
      #
      # <tt>:top</tt>::    HTML is inserted inside the element, before the
      #                    element's existing content.
      # <tt>:bottom</tt>:: HTML is inserted inside the element, after the
      #                    element's existing content.
      # <tt>:before</tt>:: HTML is inserted immediately preceding the element.
      # <tt>:after</tt>::  HTML is inserted immediately following the element.
      #
      # +options_for_render+ may be either a string of HTML to insert, or a hash
      # of options to be passed to ActionView::Base#render.  For example:
      #
      #   # Insert the rendered 'navigation' partial just before the DOM
      #   # element with ID 'content'.
      #   # Generates: Element.insert("content", { before: "-- Contents of 'navigation' partial --" });
      #   page.insert_html :before, 'content', :partial => 'navigation'
      #
      #   # Add a list item to the bottom of the <ul> with ID 'list'.
      #   # Generates: Element.insert("list", { bottom: "<li>Last item</li>" });
      #   page.insert_html :bottom, 'list', '<li>Last item</li>'
      #
      def insert_html(position, id, *options_for_render)
        content = javascript_object_for(render(*options_for_render))
        record "Element.insert(\"#{id}\", { #{position.to_s.downcase}: #{content} });"
      end

      # Replaces the inner HTML of the DOM element with the given +id+.
      #
      # +options_for_render+ may be either a string of HTML to insert, or a hash
      # of options to be passed to ActionView::Base#render.  For example:
      #
      #   # Replace the HTML of the DOM element having ID 'person-45' with the
      #   # 'person' partial for the appropriate object.
      #   # Generates:  Element.update("person-45", "-- Contents of 'person' partial --");
      #   page.replace_html 'person-45', :partial => 'person', :object => @person
      #
      def replace_html(id, *options_for_render)
        call 'Element.update', id, render(*options_for_render)
      end

      # Replaces the "outer HTML" (i.e., the entire element, not just its
      # contents) of the DOM element with the given +id+.
      #
      # +options_for_render+ may be either a string of HTML to insert, or a hash
      # of options to be passed to ActionView::Base#render.  For example:
      #
      #   # Replace the DOM element having ID 'person-45' with the
      #   # 'person' partial for the appropriate object.
      #   page.replace 'person-45', :partial => 'person', :object => @person
      #
      # This allows the same partial that is used for the +insert_html+ to
      # be also used for the input to +replace+ without resorting to
      # the use of wrapper elements.
      #
      # Examples:
      #
      #   <div id="people">
      #     <%= render :partial => 'person', :collection => @people %>
      #   </div>
      #
      #   # Insert a new person
      #   #
      #   # Generates: new Insertion.Bottom({object: "Matz", partial: "person"}, "");
      #   page.insert_html :bottom, :partial => 'person', :object => @person
      #
      #   # Replace an existing person
      #
      #   # Generates: Element.replace("person_45", "-- Contents of partial --");
      #   page.replace 'person_45', :partial => 'person', :object => @person
      #
      def replace(id, *options_for_render)
        call 'Element.replace', id, render(*options_for_render)
      end

      # Removes the DOM elements with the given +ids+ from the page.
      #
      # Example:
      #
      #  # Remove a few people
      #  # Generates: ["person_23", "person_9", "person_2"].each(Element.remove);
      #  page.remove 'person_23', 'person_9', 'person_2'
      #
      def remove(*ids)
        loop_on_multiple_args 'Element.remove', ids
      end

      # Shows hidden DOM elements with the given +ids+.
      #
      # Example:
      #
      #  # Show a few people
      #  # Generates: ["person_6", "person_13", "person_223"].each(Element.show);
      #  page.show 'person_6', 'person_13', 'person_223'
      #
      def show(*ids)
        loop_on_multiple_args 'Element.show', ids
      end

      # Hides the visible DOM elements with the given +ids+.
      #
      # Example:
      #
      #  # Hide a few people
      #  # Generates: ["person_29", "person_9", "person_0"].each(Element.hide);
      #  page.hide 'person_29', 'person_9', 'person_0'
      #
      def hide(*ids)
        loop_on_multiple_args 'Element.hide', ids
      end

      # Toggles the visibility of the DOM elements with the given +ids+.
      # Example:
      #
      #  # Show a few people
      #  # Generates: ["person_14", "person_12", "person_23"].each(Element.toggle);
      #  page.toggle 'person_14', 'person_12', 'person_23'      # Hides the elements
      #  page.toggle 'person_14', 'person_12', 'person_23'      # Shows the previously hidden elements
      #
      def toggle(*ids)
        loop_on_multiple_args 'Element.toggle', ids
      end

      # Displays an alert dialog with the given +message+.
      #
      # Example:
      #
      #   # Generates: alert('This message is from Rails!')
      #   page.alert('This message is from Rails!')
      def alert(message)
        call 'alert', message
      end

      # Redirects the browser to the given +location+ using JavaScript, in the same form as +url_for+.
      #
      # Examples:
      #
      #  # Generates: window.location.href = "/mycontroller";
      #  page.redirect_to(:action => 'index')
      #
      #  # Generates: window.location.href = "/account/signup";
      #  page.redirect_to(:controller => 'account', :action => 'signup')
      def redirect_to(location)
        url = location.is_a?(String) ? location : @context.url_for(location)
        record "window.location.href = #{url.inspect}"
      end

      # Reloads the browser's current +location+ using JavaScript
      #
      # Examples:
      #
      #  # Generates: window.location.reload();
      #  page.reload
      def reload
        record 'window.location.reload()'
      end

      # Calls the JavaScript +function+, optionally with the given +arguments+.
      #
      # If a block is given, the block will be passed to a new JavaScriptGenerator;
      # the resulting JavaScript code will then be wrapped inside <tt>function() { ... }</tt>
      # and passed as the called function's final argument.
      #
      # Examples:
      #
      #   # Generates: Element.replace(my_element, "My content to replace with.")
      #   page.call 'Element.replace', 'my_element', "My content to replace with."
      #
      #   # Generates: alert('My message!')
      #   page.call 'alert', 'My message!'
      #
      #   # Generates:
      #   #     my_method(function() {
      #   #       $("one").show();
      #   #       $("two").hide();
      #   #    });
      #   page.call(:my_method) do |p|
      #      p[:one].show
      #      p[:two].hide
      #   end
      def call(function, *arguments, &block)
        record "#{function}(#{arguments_for_call(arguments, block)})"
      end

      # Assigns the JavaScript +variable+ the given +value+.
      #
      # Examples:
      #
      #  # Generates: my_string = "This is mine!";
      #  page.assign 'my_string', 'This is mine!'
      #
      #  # Generates: record_count = 33;
      #  page.assign 'record_count', 33
      #
      #  # Generates: tabulated_total = 47
      #  page.assign 'tabulated_total', @total_from_cart
      #
      def assign(variable, value)
        record "#{variable} = #{javascript_object_for(value)}"
      end

      # Writes raw JavaScript to the page.
      #
      # Example:
      #
      #  page << "alert('JavaScript with Prototype.');"
      def <<(javascript)
        @lines << javascript
      end

      # Executes the content of the block after a delay of +seconds+. Example:
      #
      #   # Generates:
      #   #     setTimeout(function() {
      #   #     ;
      #   #     new Effect.Fade("notice",{});
      #   #     }, 20000);
      #   page.delay(20) do
      #     page.visual_effect :fade, 'notice'
      #   end
      def delay(seconds = 1)
        record "setTimeout(function() {\n\n"
        yield
        record "}, #{(seconds * 1000).to_i})"
      end

      # Starts a script.aculo.us visual effect. See
      # ActionView::Helpers::ScriptaculousHelper for more information.
      def visual_effect(name, id = nil, options = {})
        record @context.send(:visual_effect, name, id, options)
      end

      # Creates a script.aculo.us sortable element. Useful
      # to recreate sortable elements after items get added
      # or deleted.
      # See ActionView::Helpers::ScriptaculousHelper for more information.
      def sortable(id, options = {})
        record @context.send(:sortable_element_js, id, options)
      end

      # Creates a script.aculo.us draggable element.
      # See ActionView::Helpers::ScriptaculousHelper for more information.
      def draggable(id, options = {})
        record @context.send(:draggable_element_js, id, options)
      end

      # Creates a script.aculo.us drop receiving element.
      # See ActionView::Helpers::ScriptaculousHelper for more information.
      def drop_receiving(id, options = {})
        record @context.send(:drop_receiving_element_js, id, options)
      end

      private
      def loop_on_multiple_args(method, ids)
        record(ids.size>1 ?
                   "#{javascript_object_for(ids)}.each(#{method})" :
                   "#{method}(#{::ActiveSupport::JSON.encode(ids.first)})")
      end

      def page
        self
      end

      def record(line)
        returning line = "#{line.to_s.chomp.gsub(/\;\z/, '')};" do
          self << line
        end
      end

      def render(*options_for_render)
        old_format = @context && @context.template_format
        @context.template_format = :html if @context
        Hash === options_for_render.first ?
            @context.render(*options_for_render) :
            options_for_render.first.to_s
      ensure
        @context.template_format = old_format if @context
      end

      def javascript_object_for(object)
        ::ActiveSupport::JSON.encode(object)
      end

      def arguments_for_call(arguments, block = nil)
        arguments << block_to_function(block) if block
        arguments.map { |argument| javascript_object_for(argument) }.join ', '
      end

      def block_to_function(block)
        generator = self.class.new(@context, &block)
        literal("function() { #{generator.to_s} }")
      end

      def method_missing(method, *arguments)
        JavaScriptProxy.new(self, method.to_s.camelize)
      end
    end
  end

  # Yields a JavaScriptGenerator and returns the generated JavaScript code.
  # Use this to update multiple elements on a page in an Ajax response.
  # See JavaScriptGenerator for more information.
  #
  # Example:
  #
  #   update_page do |page|
  #     page.hide 'spinner'
  #   end
  def update_page(&block)
    JavaScriptGenerator.new(@template, &block).to_s
  end

  # Works like update_page but wraps the generated JavaScript in a <script>
  # tag. Use this to include generated JavaScript in an ERb template.
  # See JavaScriptGenerator for more information.
  #
  # +html_options+ may be a hash of <script> attributes to be passed
  # to ActionView::Helpers::JavaScriptHelper#javascript_tag.
  def update_page_tag(html_options = {}, &block)
    javascript_tag update_page(&block), html_options
  end

  protected
  def options_for_ajax(options)
    js_options = build_callbacks(options)

    content_type = if options[:headers]
                     key, val = options[:headers].find {|k, v| k.to_s.downcase == 'content-type'}
                     options[:headers].delete(key)
                   end

    js_options['asynchronous'] = options[:type] != :synchronous
    js_options['requestHeaders'] = quote_hash(options[:headers]) if options[:headers]
    js_options['contentType'] = "'#{content_type}'" if content_type
    js_options['method']       = method_option_to_s(options[:method]) if options[:method]
    js_options['insertion']    = "'#{options[:position].to_s.downcase}'" if options[:position]
    js_options['evalScripts']  = options[:script].nil? || options[:script]

    if options[:form]
      js_options['parameters'] = 'Form.serialize(this)'
    elsif options[:submit]
      js_options['parameters'] = "Form.serialize('#{options[:submit]}')"
    elsif options[:with]
      js_options['parameters'] = options[:with]
    end

    if protect_against_forgery? && !options[:form]
      if js_options['parameters']
        js_options['parameters'] << " + '&"
      else
        js_options['parameters'] = "'"
      end
      js_options['parameters'] << "#{request_forgery_protection_token}=' + encodeURIComponent('#{escape_javascript form_authenticity_token}')"
    end

    options_for_javascript(js_options)
  end

  def quote_hash(hash)
    "{#{hash.keys.map { |key| "'#{key}':'#{hash[key]}'" }.join(', ')}}"
  end

  def method_option_to_s(method)
    (method.is_a?(String) and !method.index("'").nil?) ? method : "'#{method}'"
  end

  def build_observer(klass, name, options = {})
    if options[:with] && (options[:with] !~ /[\{=(.]/)
      options[:with] = "'#{options[:with]}=' + encodeURIComponent(value)"
    else
      options[:with] ||= 'value' unless options[:function]
    end

    callback = options[:function] || remote_function(options)
    javascript  = "new #{klass}('#{name}', "
    javascript << "#{options[:frequency]}, " if options[:frequency]
    javascript << "function(element, value) {"
    javascript << "#{callback}}"
    javascript << ")"
    javascript_tag(javascript)
  end

  def build_callbacks(options)
    callbacks = {}
    options.each do |callback, code|
      if CALLBACKS.include?(callback)
        name = 'on' + callback.to_s.capitalize
        callbacks[name] = "function(request){#{code}}"
      end
    end
    callbacks
  end

  def options_for_javascript(options)
    if options.empty?
      '{}'
    else
      "{#{options.keys.map { |k| "#{k}:#{options[k]}" }.sort.join(', ')}}"
    end
  end


end

